This invention relates to a variable transmission (IVT) machine in which the ratio of an output rotational speed to an input rotational speed, of the machine, is adjustable in increments.
The specification of International application number PCT/ZA2004/000023 (herein the “earlier specification”) describes an infinitely variable transmission in which the ratio of output speed to input speed can be incrementally varied. The machine is, however, of complex construction and is not compact. Another adverse factor is that the tension in a drive chain between input and output drives of the machine can vary in an unsatisfactory manner depending, for example, on whether a prime mover is operating on the machine or if the machine is being used in a braking mode.
The present invention aims to provide a variable transmission machine which is compact and which can transmit substantial power and in which the ratio of output to input speed can be varied in a large number of small increments so that, for practical purposes, the output speed does not change in a step-wise manner. It is also an object of the present invention to provide an integrated chain tensioning system with a simple, robust and integrated mechanical shifting mechanism thereby to avoid the use of hydraulic arrangements. The last mentioned aspect is of particular significance for, by way of example, a hydraulic pump, in an IVT machine which has a hydraulic control system, runs continuously and can consume up to 5% or 6% of the available power.